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145

Chapter 6. Nitrate Losses to Surface Water Through Subsurface,

Tile Drainage

G . W . Randall

a

and M.J. Goss

b

a

Southern Research and Outreach Center, University of Minnesota, Waseca,

Minnesota, USA

b

Kemptville Campus, University of Guelph, Kemptville, Ontario, Canada

1 . INTRODUCTION

Subsurface drainage is a common water management practice in highly produc-

tive agricultural areas with poorly drained soils that have seasonally perched water

tables or shallow groundwater. This management practice increases crop productiv-

ity, reduces risk, and improves economic returns to crop producers. Eight states in

the North Central Region of the United States of America, (Illinois, Indiana, Iowa,

Michigan, Minnesota, Missouri, Ohio, and Wisconsin) form one of the most highly

drained regions in the country (Zucker and Brown, 1998). In total, they account for

over 20.6 million hectares or 37% of the total cropland drained by surface and sub-

surface drainage ( Fausey et al., 1995 ). Substantial concentrations of nutrients can be

contained in subsurface tile drainage water and, depending on the amount of water

flow; large losses from the soil may occur ( Baker et al., 1975 ; Baker and Johnson,

1981 ; Randall, 1998 ; Jaynes et al., 2001 ; Dinnes et al., 2002 ).

Societal concerns about the quality of river water and its ecological impact

on receiving bodies, such as lakes and coastal marine estuaries on the continental

shelf, have escalated since the late 1980s. Hypoxia, a condition where the concen-

tration of dissolved oxygen is  2 mg/L, has been known to exist in portions of

the world ’ s oceans and shallow seas for several decades (Diaz and Rozenberg, 1995;

Diaz, 2001 ), but seasonal hypoxia has recently been reported in the Gulf of Mexico

off the coast of Louisiana ( Rabalais et al., 1994 ). The cause of hypoxia in this salt

water system has been linked indirectly to the load of nutrients, primarily nitro-

gen (N), delivered to the Gulf via the Mississippi River drainage basin ( Turner and

Rabalais, 1994 ; Rabalais et al., 1996 ). Nitrate concentrations in the Mississippi

River are generally greatest in the tributaries emanating from Illinois, Iowa, and

Minnesota and vary seasonally, usually being larger in winter, spring, and early

summer and least in late summer and early autumn ( Antweiler et al., 1995 ). Burkart

and James (1999) determined the hydrologic units with the largest residual N con-

tributions available to streams and largest total N loss rates are located in the Upper

Nitrogen in the Environment: Sources, Problems, and Management

J.L. Hatfield and R.F. Follett (Eds)

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146 Nitrogen in the Environment

Mississippi River and the Ohio River Basins where row crops, particularly corn and

soybean, dominate the landscape.

This chapter focuses on the following:

1. the linkage between subsurface tile drainage of agricultural lands and nitrate

in surface waters, and

2. the effect of uncontrollable factors (precipitation and soil mineralization) and

controllable factors (cropping system, rate and time of N application, nitrifi-

cation inhibitors, tillage, and drain tile spacing and depth) on nitrate losses to

subsurface drainage.

2 . ROLE OF AGRICULTURE

Agricultural drainage water has been identified as a major contributor to the

nitrate-N loading of receiving waters. Research conducted at widely different scales

of watershed basins point to the fact that agricultural systems do affect nitrate levels

in river waters. Similarly, long-term field plot research has demonstrated the effects of

crop and nutrient management practices on edge-of-field loss of nitrate to subsurface

drainage water.

2.1 . Watershed Basins

Omernik (1977) reported that total N concentrations were nearly nine times

greater downstream from agricultural lands than from forested areas with the

largest concentrations being found in the Corn Belt States. Nitrate-N concentra-

tions in stream water collected between 1984 and 1993 for a portion of the Upper

Mississippi River Basin were significantly greater from those rivers which drained

a large percentage of agricultural land (2–6 mg/L) compared to those draining land

with a larger percentage under forest (0.1–0.5 mg/L). In the Mississippi River, mean

concentrations (1.8–2.5 mg/L) were significantly greater downstream of the con-

fluence with a major river draining an agricultural watershed than those upstream

(0.2–0.9 mg/L) ( Kroening, 1996 ).

Subsurface drains were suggested by Martin et al. (1996) as the source of high

levels of nitrate in the stream water of the White River Basin of Indiana. Subsurface

tile drainage directly affected water quality in a small central Indiana stream (Sugar

Creek) by transporting soil pore water and shallow groundwater containing high

concentrations of nitrate to the creek ( Fenelon and Moore, 1998 ). When tile drains

were flowing (typically December through July), elevated nitrate-N concentrations

(2–10 mg/L) in the creek correlated with large nitrate-N concentrations (2–23 m g / L )

in tile drains discharging to the creek. When tile drains went dry, nitrate concentra-

tions in the creek were small, indicating most groundwater discharge to the creek

consisted of old or denitrified water. Although agrichemicals in Sugar Creek and

many similar small streams throughout the Midwest are not considered a problem

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Nitrate Losses to Surface Water Through Subsurface, Tile Drainage 147

to many people, in part because stream water is not used to supply drinking water,

elevated nitrate concentrations may be undesirable because of:

1. contamination of downstream public water resources such as reservoirs

( Scribner et al., 1996 ),

2. economic loss suffered by farmers who lose fertilizer to streams,

3. potential stresses on fish communities, and

4. eutrophication of downstream surface waters, for example, the Gulf of Mexico,

receiving discharge water in part from many small drainage basins ( Fenelon

and Moore, 1998 ).

In Illinois, elevated concentrations of nitrate-N (5–49 mg/L) were found in four

monitored drainage tiles in the Embarras River watershed during a 6-year period,

and these concentrations were synchronous with nitrate concentrations in the

Embarras River ( David et al., 1997 ). These authors later estimated that Illinois con-

tributed 15% of the annual total N load of the Mississippi River, and that any reduc-

tion strategy in Illinois must address agricultural sources ( David and Gentry, 2000 ).

Generally, in the United States of America, rivers with higher concentrations

of nitrate seem to be surrounded by landscapes and watershed basins with similar

general characteristics. They are:

1. humid/high rainfall conditions,

2. soils high in organic matter,

3. poorly drained, fine-textured soils needing artificial subsurface drainage for

optimum crop production, and

4. domination by intensive corn and soybean agricultural systems.

2.2 . Classical Field Studies

Monitoring of nitrate losses in subsurface drainage water from agricultural

fields began in England in the 1850s ( Lawes et al., 1882 ). About 100 years elapsed

before additional drainage studies were installed in both Europe and North America.

These drainage facilities have been used to monitor tile effluents for assessing the

impact of agricultural management practices on surface and groundwater qual-

ity ( Hallberg et al., 1986 ; Kanwar et al., 1988 ; Addiscott et al., 1991 ; Goss et al.,

1998 ). Subsurface drains integrate the effects of spatial variability on a field scale

and may be a better tool for studying agricultural impacts on water quality than

measurement methods such as suction cups and soil cores ( Richard and Steenhuis,

1988 ). However, solute concentrations in subsurface drain flow have been shown to

not respond immediately to changes in chemical application rates or residual levels

in the soil ( Jury, 1975a, b ; Gast et al., 1978 ; Baker and Johnson, 1981 ). Some time

lag is exhibited due to travel time depending on drain spacing, soil hydraulic prop-

erties, and precipitation.

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148 Nitrogen in the Environment

3 . FACTORS AFFECTING NITRATES IN SUBSURFACE DRAINAGE

The primary factors that influence the nitrate content of surface waters draining

agricultural production landscapes can be divided into two categories – uncontrol-

lable and controllable. Uncontrollable factors include: (1) precipitation, and (2) soil

organic matter mineralization, which to some degree can be manipulated, for exam-

ple by tillage. Controllable factors include those agricultural management prac-

tices that are used by crop producers to best fit the needs of their own enterprise.

The controllable factors include: cropping system used, rate of N applied, time of

N application, placement method, use of a nitrification inhibitor, tillage system, and

drain tile spacing and depth.

3.1 . Precipitation

Loading of nitrate-N into surface water is a function of transport volume (amount

of water) and nitrate-N concentration in the transported water. Since nitrate concen-

trations of drainage water within a year are normally fairly stable, with characteristic

levels for each cropping system, the annual variation in nitrate-N flux lost through

subsurface drains depends primarily on the volume of water drained ( Bolton et al.,

1970 ; Letey et al., 1977 ; Goss et al., 1998 ; Tomer et al., 2003 ). Exceptions to this

premise exist in particular climate/cropping scenarios as was shown for winter

cereal grain production on clay soils in the United Kingdom. Nitrate-N concentra-

tions in November often exceeded 50 mg/L but decreased to between 1 and 5 m g / L

in late February and March ( Harris et al., 1984 ). The amount of drainage water leav-

ing the landscape is largely a function of climate and soil properties – precipitation,

texture, structure, and infiltration rate. Drainage is further influenced by the tempo-

ral distribution of precipitation within a year and the amount of annual or growing

season precipitation that occurs. For instance, an 80-mm rainfall in the spring, when

evapotranspiration (ET) losses are small and moisture in the soil above the drains is

likely near field capacity, will have a much greater effect on drainage volume than

the same rainfall during the middle of the summer when daily ET losses are high and

soil is relatively dry. In the former scenario, storage capacity is minimal and drainage

water carrying nitrates is plentiful. A significant storage reservoir exists in the soil in

the latter scenario, and subsurface drainage is less likely to occur.

The effect of climate on subsurface drainage volume was clear in a series of tile

drainage studies from Minnesota. Annual tile drainage in an 11-year study con-

ducted with continuous corn ranged from 26 to 618 mm/year with an average of

297 mm ( Randall and Iragavarapu, 1995 ). Drainage was least in 1989 when grow-

ing season precipitation was 35% below normal and greatest in 1991 when growing

season precipitation was 51% above normal ( Table 1 ). In addition, drainage in the

3-year dry period (1987–1989) averaged only 43 mm compared to the following

3-year wet period (1990–1992) when drainage averaged 549 mm. A 6-year study

showed no tile drainage in 1988 and 1989 when annual precipitation was 69% and 76%

of normal, respectively ( Randall et al., 1997 ). Drainage from the corn and soybean

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Nitrate Losses to Surface Water Through Subsurface, Tile Drainage 149

row-crop systems averaged 22 mm in 1990, 223 mm in 1991, 143 mm in 1992, and

469 mm in 1993 ( Table 2 ). Annual precipitation in those 4 years was 95%, 125%,

117%, and 160% of normal, respectively. Data from these studies clearly indicate

the strong relationship between annual or growing season precipitation and volume

of subsurface, tile drainage.

Drainage volume and nitrate losses have been shown to be affected also by the

temporal distribution of annual precipitation within a year coupled with ET and

winter temperatures. Subsurface drainage occurs primarily during the late fall, win-

ter, and early spring in those geographic areas where soils are not frozen throughout

the winter ( Kladivko et al., 1991, 1999, 2004 ; Drury et al., 1993 ; Goss et al., 1993,

1998 ; Fenelon and Moore, 1998 ). Between 78% and 100% of annual flow occurred

after harvest during the dormant season of October to May in Ontario ( Patni et al.,

1996 ). An 8-year study in the United Kingdom showed 84% of the nitrate lost in

subsurface drainage occurred between fall seeding of annual cereals and the first

application of N in the spring ( Goss et al., 1988 ). In Iowa, 45–85% of the annual

nitrate loss through subsurface drainage occurred in the spring and fall when crops

were not actively growing ( Bjorneberg et al., 1996 ). About 63% of the annual

N load occurred in November through March and 78% in November through April

in Indiana ( Kladivko et al., 2004 ). In Minnesota where soils usually remain fro-

zen from early December through late March, subsurface drainage occurs primarily

between mid-April and early July ( Gast et al., 1978 ). The 3-month period of April,

Table 1.

Influence of growing season precipitation on drainage volume and annual nitrate-N

losses.

April–October Nitrate-N

Year Rainfall

1

(mm) Drainage (mm)

Concentration

2

(mg/L)

Lost (kg/ha)

1986 796 402 14 55

1987 586 42 9 4

1988 426 46 15 6

1989 414 26 12 2

1990 789 486 24 112

1991 961 618 24 139

1992 726 417 14 55

Adapted from Randall and Iragavarapu (1995) .

1

1961–1990 Normal  639 m m .

2

Annual flow-weighted concentration.

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150 Nitrogen in the Environment

May, and June accounted for 71% of the annual drainage volume ( Figure 1 ) and

73% of the annual nitrate loss from corn rotated with soybean in a 15-year (1987–

2001) Minnesota study ( Randall, 2004 ). The large proportion of annual subsurface

drainage flow occurring from late fall through the spring without an actively grow-

ing crop has profound implications on N management, especially fall-applied N and

residual nitrate in the soil profile after harvest.

Nitrate-N concentrations in subsurface drainage water do not appear to vary

consistently with daily drain flow volumes but do show seasonal and yearly trends

( Harris et al., 1984 ; Kladivko et al., 1991 ). A linear relationship between the vol-

ume of subsurface drainage in winter and the mass of nitrate leached was reported

by Kolenbrander (1969) and Goss et al. (1998) for Northern European conditions.

The relationship observed for the spring and summer by Goss et al. (1998) indicated

smaller losses under winter wheat ( Triticum aestivum L.) than in the Minnesota

studies with corn. Factors affecting this variability include crop uptake of N, resid-

ual nitrate in the soil from the previous year, and amount and distribution of rainfall.

Goolsby et al. (2001) noted that the concentration and flux of nitrate in rivers of the

Mississippi River Basin tend to be the largest in the spring when stream flow is

greatest. Increased flows and elevated concentrations in agricultural tile drains were

suggested as contributing to this relationship. Annual average nitrate-N concentra-

tions in the Des Moines River from 1980 through 1990 ranged from 2.0 mg/L in 1989

to 9.1 mg/L in 1982, with an 11-year average of 5.6 mg/L ( Keeney and DeLuca,

1993 ). Maximum daily nitrate-N concentration ranged from 5.9 mg/L in 1989 to

14.5 mg/L in 1982.

Table 2.

Amount of subsurface drainage water as affected by annual precipitation and

cropping system (all values are given in millimeters).

Year

Crop System 1988 1989 1990 1991 1992 1993

Continuous Corn 0 0 20 178 132 442

Corn-Soybean 0 0 18 274 122 488

Soybean-Corn 0 0 28 218 175 478

Alfalfa 0 0 0 41 56 320

CRP

1

0 0 0 43 86 510

Average of Row Crop Systems 0 0 22 223 143 469

Average of Perennial Crop Systems 0 0 0 42 71 415

% of Normal Annual Precipitation

2

69 76 95 125 117 160

Adapted from Randall et al. (1997) .

1

CRP  Conservation Reserve Program (mixture of grass and alfalfa).

2

1961–1990 Normal  647 m m .

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Nitrate Losses to Surface Water Through Subsurface, Tile Drainage 151

Nitrate-N losses in subsurface tile drainage water vary greatly among years due

primarily to differences in annual and growing season precipitation. Twenty five stud-

ies conducted for 2–11 years in North America and Europe show annual nitrate-N

losses ranging from 0 to 139 kg/ha/year ( Table 3 ). Moreover, a few days with high-

flow events can lead to most of the annual nitrate loss in some years ( David et al.,

1997 ). Because of the influence of precipitation on nitrate loss, long-term drain-

age research that integrates the effect of climatic variability is vital to our ability

to predict nutrient losses from agricultural production systems through subsurface

drainage.

Nitrate-N concentrations and losses are also greatly affected by dry and wet cli-

matic cycles ( Logan et al., 1994 ; Randall, 1998 ). These effects are seen at the river

scale as well as at the edge-of-field scale. In Iowa, excessive nitrate-N concentrations

in 1990 in the Raccoon River followed 2 years of less-than-normal precipitation in

1988 and 1989 ( Lucey and Goolsby, 1993 ). Large concentrations persisted in the

water as stream flow decreased to base flow rates, implying that substantial quan-

tities of nitrate-N were being leached from the soil and transported by subsurface

flow in 1990. Drainage plots in Minnesota with continuous corn grown from 1986

through 1992 clearly showed the edge-of-field effects of dry and wet climatic cycles

( Randall, 1998 ). Annual flow-weighted nitrate-N concentration in 1986 was 14 mg/L

while drainage totaled 402 mm ( Table 1 ). Dry conditions during 1987–1989, when

April to October rainfall was 25% below normal, resulted in  50 mm drainage

Month

Jan Feb Mar

Apr May Jun

Jul Aug

Sep Oct Nov Dec

Percent of annual discharge

0

5

10

15

20

25

30

Figure 1 . Monthly distribution of subsurface tile drain discharge averaged across a

15-year (1987–2001) period for a corn–soybean rotation.

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152 Nitrogen in the Environment

Table 3.

Range of annual nitrate-N losses in subsurface tile drainage water in European and

North American research studies.

Source Location

Years

Studied Crop(s)

1

Nitrate-N Loss

(kg/ha/year)

Gast et al., 1978 Minnesota, USA 3 CC 6 to 25

Bergstrom, 1987 Sweden 4 Barley  1 to 27

Kladivko et al., 1991

2

Indiana, USA 3 CC 28 to 31

Drury et al., 1993 Ontario, CAN 3 CC 7 to 29

Goss et al., 1993 England 8 Wheat 6 to 73

Logan et al., 1994 Ohio, USA 4 C–Sb  1 to 86

Randall and Iragavarapu,

1995

Minnesota, USA 11 CC 1 to 139

Bjorneberg et al., 1996

3

Iowa, USA 3 CC 19 to 100

3 C –Sb 17 to 53

3 Sb –C 8 to 52

Patni et al., 1996 Ontario, CAN 4 CC 10 to 39

Randall et al., 1997 Minnesota, USA 6 CC 0 to 91

C– Sb 0 to 88

Sb –C 0 to 81

Bjorneberg et al., 1998

3

Iowa, USA 3 C–Sb 3 to 33

Catt et al., 1998 England 4 Mixed

4

1 to 48

Cereals

5

4 to 22

Grass 1 to 10

Jaynes et al., 1999 Iowa, USA 4 C–Sb 5 to 51

Kladivko et al., 1999

2

Indiana, USA 3 CC 22 to 50

Watson et al., 2000 Ireland 9 Ryegrass 16 to 52

Randall et al., 2000 Minnesota, USA 4 CC 12 to 20

Sogbedji et al., 2000 New York, USA 2 CC 6 to 35

Randall and Mulla, 2001 Minnesota, USA 5 CC 8 to 38

Jaynes et al., 2001 Iowa, USA 4 C–Sb 13 to 61

Bakhsh et al., 2002 Iowa, USA 6 C –Sb 3 to 46

6 Sb –C 3 to 37

Tomer et al., 2003 Iowa, USA 8 C–Sb 2 to 59

Randall et al., 2003 Minnesota, USA 7 C –Sb 0 to 122

7 Sb –C 0 to 79

Hofmann et al., 2004 Indiana, USA 6 CC 5 to 50

(Continued)

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Hatfield J.L., Gandini A. (eds.) Nitrogen in the Environment

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